The mechanism for controlling the traits of plants (e.g., morphogenesis of flowers) has been studied in methodologies of molecular biology and molecular genetics using Arabidopsis (Arabidopsis thaliana), Antirrhinum (Antirrhinum majus), and Petunia (Petunia hybrida). Particularly, Petunia is often chosen as a research material. The reason is that Petunia has great value as a garden plant, there are a number of varieties, it is easy to transform, the flower is large and viewable, and there is a large amount of accumulated genetic knowledge, for example (Hiroshi Takatsuji, “Molecular Mechanism Determining Shapes of Plants”, Saibo-kogaku, Syokubutsu-saibo-kogaku Series (Syujyunsya), pp. 96–106 (1994)).
It is considerably important to identify promoters having a tissue-specific expression activity. For example, if a heterogenous gene is desired to be tissue-specifically expressed, an expression cassette is constructed in which the heterogenous gene of interest is linked downstream of a promoter having an expression activity specific to a target tissue (i.e., the heterogenous gene of interest is arranged so as to be expressed under the control of the promoter). The expression cassette is introduced into a plant, allowing specific expression of the heterogenous gene of interest in the target tissue. Specific expression of a heterogenous gene in a plant tissue of interest can confer a modified trait to the plant and therefore has great value in research and horticulture.
For example, when a tissue-specific promoter activity can be found in a pistil tissue, a heterogenous gene can be expressed specifically in the pistil tissue by operatively linking the gene to the promoter and introducing it into a plant. It is believed that, for example, the traits of female sterility and self-incompatibility can be conferred to a plant by utilizing such pistil tissue-specific expression.
It is known that pollination induces synthesis of ethylene which accelerates wilting and shortens the life of flowers. It is also known that generally, pollination cannot induce ethylene synthesis in female-sterile plants and therefore the life of such flowers is long. It is considered that conferring female sterility to flowering plants of garden varieties may lead to an improved lifetime of the flowering plants. Therefore, technology for conferring female sterility to a plant has a great importance to the horticulture industry.
Conventionally, in order to confer the trait of female sterility to a plant, mutation techniques, such as a heavy ion beam irradiation method, have been tried. The following biotechnological methods have also been reported: (1) expression of diphtheria toxin using a promoter specific to the stigma tissue of Brassica (Kandasamy, M. K. et al., Plant Cell, 5,263–275 (1993)); and (2) expression of barnase (an enzyme having an activity of causing cell death) using a promoter specific to the stigma tissue of tobacco (Goldman, M. H. et al., EMBO J., 13, 2976–2984 (1994)).
Self-incompatibility is an important trait in terms of the efficiency of crossbreeding. A technique for conferring self-incompatibility to tobacco (Nicotiana) has been developed in which a gene having an ability to remove pollen (S-RNase gene) is expressed specifically in the pistil transmitting tissue using a promoter for Chi2;1 derived from tomato (Harikrishna, K. et al., Plant Mol. Biol., 30, 899–911 (1996)).
As described above, the identification of promoters having an expression activity specific to pistil tissue is important not only for scientific research but also for practical applications. If such a promoter can be isolated, it can be very useful for modification of traits of useful plants, such as garden varieties.